It is widely known that tobacco smoke contains mutagenic and carcinogenic compounds which cause substantial morbidity and mortality to smokers. Examples of such substances include polycyclic aromatic hydrocarbons (PAH) and nitrosamines.
Polycyclic aromatic hydrocarbons appear to cause toxicity by intercalating within DNA molecules. Nitrosamines are electrophilic, alkylating agents which are potent carcinogens. Nitrosamines are not present in fresh or green tobaccos and are not formed during combustion. They are instead formed by reactions involving free nitrate during processing and storage of tobacco, or by the post-inhalation, metabolic activation of secondary amines present in tobacco smoke.
Attempts to reduce the amount of toxic and mutagenic compounds that reach the smoker include tobacco smoke filters positioned between the burning tobacco and the smoker. Conventional filters are made of cellulose acetate, with or without activated charcoal. These conventional filters, however, are only partially effective in reducing the amount of toxic and mutagenic compounds reaching the smoker. Further, conventional filters disadvantageously remove flavor compounds, thereby decreasing acceptance by the smoker.
There is, therefore, a need for an improved filter for a smokable device that substantially removes toxic and mutagenic compounds from tobacco smoke. Further, there is a need for an improved filter which allows the passage of flavor compounds while substantially removing toxic and mutagenic compounds from tobacco smoke. Such an improved filter would preferably be simple and inexpensive to manufacture, and convenient to use.
The present invention is directed to a tobacco smoke filter that meets these needs. In one embodiment, the filter comprises a porous substrate comprising dry water and a porphyrin dispersed therein. In a preferred embodiment, the porphyrin is a copper-containing porphyrin, such as copper phthalocyanine. In other preferred embodiments, the porous substrate further comprises microcapsules. In particularly preferred embodiments, the microcapsules comprise one or more substances selected from the group consisting of chlorophyllin, methylcellulose, sodium pyroglutamate and a vegetable oil. The porous substrate can further comprise sodium pyroglutamate.
In another preferred embodiment, there is provided a method of making a filter according to the present invention. The method comprises (a) providing a porous substrate and (b) dispersing dry water and a porphyrin therein.
In another preferred embodiment, there is provided a smokable device comprising the filter of the present invention. In yet another preferred embodiment, there is provided a method of making a smokable device. The method comprises (a) providing a filter of the present invention and (b) affixing the filter to a body of divided tobacco.
According to one embodiment of the present invention, there is provided a filter for tobacco smoke. The filter can be provided in combination with cigarettes or cigars or other smokable devices containing divided tobacco, Preferably, the filter is secured to one end of the smokable device, positioned such that smoke produced from the tobacco passes into the filter before entering the smoker. The filter can also be provided by itself, in a form suitable for attachment to a cigarette, cigar, pipe, or other smokable device.
The filter according to the present invention advantageously removes a significant proportion of mutagens and carcinogens from cigarette smoke. The filter further retains satisfactory or improved smoke flavor, nicotine content, and draw characteristics. The filter is designed to be acceptable to the user, being neither cumbersome nor unattractive as are commercially made filters which are designed to add onto the ends of premade cigarettes. Further, filters according to the present invention can be made of inexpensive, safe and effective components, and can be manufactured with only minor modifications of standard cigarette manufacturing machinery.
According to one embodiment of the present invention, the filter comprises a porous substrate. The porous substrate can be any nontoxic material suitable for use in filters for smokable devices that are also suitable for incorporation with the other substances according to embodiments of the present invention. Such porous substrates include cellulosic fiber such as cellulose acetate, cotton, wood pulp, and paper; and polyesters, polyolefins, ion exchange materials and other materials as will be understood by those with skill in the art with reference to the disclosure herein.
According to one embodiment of the present invention, the filter comprises at least one humectant, with or without other substances disclosed herein. The humectant is capable of absorbing moisture from tobacco smoke and releasing it into the porous substrate in order to wet-filter tobacco smoke that passes through the filter. Among other advantages, wet-filtration systems according to the present invention help remove particulate matter from tobacco smoke and can be made integral with a tobacco containing product.
The humectant can be any suitable humectant. For example, the humectant can be selected from the group consisting of glycerol, sorbitol, propylene glycol, sodium lactate, calcium chloride, potassium phosphate, sodium pyrophosphate or sodium polyphosphate, calcium citrate, calcium gluconate, potassium citrate, potassium gluconate, sodium tartrate, sodium potassium tartrate, and sodium glutamate.
In a preferred embodiment, the humectant incorporated into the filter is sodium pyroglutamate (also known as sodium 2-pyrrolidone-5-carboxylate or NaPCA). Advantageously, sodium pyroglutamate is nontoxic, effective at removing charged particles from tobacco smoke and functions as a humectant in the temperature range of tobacco smoke. Further, it is nonhazardous, stable, simple to manufacture and convenient to use. Sodium pyroglutamate has the following structure: 
Filters according to the present invention are simple and inexpensive to manufacture. In one method of manufacture, a solution containing the humectant, such as sodium pyroglutamate, is prepared. Then, the porous substrate is wetted with the solution. The wetted substrate is then dried, leaving a residue of the humectant dispersed on or in the porous substrate. In a preferred embodiment, the humectant is present in an amount of from about 5 to about 60% by dry weight of the filter.